Some difficulty has been experienced when a liquid fuel such as diesel oil is provided to an internal burner type ultra-high velocity flame jet apparatus of the type set forth in my earlier U.S. Pat. No. 2,990,653 entitled "Method and Apparatus for Impacting a Stream of High Velocity Against the Surface to be Treated" issuing July 4, 1961. The apparatus of that patent takes the form of an air cooled double or triple wall cylindrical internal burner whose interior forms a combustion chamber and which is provided with a reduced diameter flame jet nozzle at one end thereof. At the opposite end, a fuel/air mixture is ignited, the combustion chamber receiving a continuous pressurized flow of air which mixes with the fuel and is ignited at that end of the chamber to materially increase the temperature of the continuous flowing stream prior to discharge and pressure reduction, at high velocity, through the nozzle bore. In the apparatus of that patent, combustion of a fuel/air mixture is effected by the incorporation of a spark plug and thus a spark ignition system within the cylindrical internal burner body, specifically with the spark plug at right angles to the flow axis of the stream passing through the combustion chamber. The spark ignition system is characterized by a spark plug in which one central electrode is surrounded by a second electrode, and wherein some of the compressed air employed in cooling the sidewall of the internal combustion chamber is permitted to flow through the annular space between the electrodes.
This spark ignition system, while reliably igniting gaseous fuel, proved unreliable when used with liquid fuels. Ignition was effected by arcing between the centrally located first electrode within an annular space about double the diameter of the first electrode arcing rod element and the second electrode surrounding the arcing rod. A spark was struck between these electrodes and elongated into a "flame" by causing a small portion of the compressed air employed in cooling the double wall internal burner to flow through the annular space between the electrodes.
It is, therefore, a primary object of the present invention to provide an improved method and apparatus for effecting ignition of an internal burner type ultra-high velocity flame jet apparatus for effectively burning a liquid fuel such as diesel oil, insuring initial ignition of the liquid fuel by the introduction of a gas having an oxygen content in excess of that of natural air, extending the spark between electrodes of the spark plug employed in the ignition process, and feeding in addition thereto a portion of the compressed air normally supplied to the combustion chamber, through an annular gap between the spark plug electrodes both during ignition and during normal extended operation of the flame jet apparatus.
It is a further object of this invention to provide an improved flame jet apparatus of this type, where the spark plug assembly is coaxially incorporated within the internal burner at the end of the combustion chamber opposite that of the flame jet nozzle, and wherein the fuel flow is introduced directly into the region of the extended spark bearing the oxygen enriched gas.
It is a further object of this invention to provide an improved internal burner type ultra-high velocity flame jet apparatus wherein an enriching flow of oxygen is supplied both to the area of extended spark between spaced electrodes of the internal burner and to the main compressed air flow stream entering the combustion chamber remote from the spark plug and provided as a flame reactant.